Astrolabes Made by Individuals
Following are descriptions and pictures of astrolabes made by individuals. They are presented in the order received. Send me pictures and a detailed description of any astrolabes you have made if you would like for them to be included here.
Mariner's Astrolabe by John Clark, Cheddar, UK (firstname.lastname@example.org)
John Clark, who was a toolmaker, has made a lovely Mariner's Astrolabe. His description of the project follows.
I designed the complete astrolabe on Autocad LT using holes for the calibration marks as I had no means of engraving any line detail. The degree holes are 1mm dia on a 275 pcd. I used these dimensions to give an approximate 1mm wide gap between the holes for easy reading. The 5 and 10 degree marks are 2mm dia. I drilled them all in one three hour session using a rotary table on a Bridgeport mill.
The frame profile was roughly hand sawn to shape and then profiled milled. The frame, arm and hanging ring are aircraft grade aluminium. The vee notched sights and screws are brass. The centre pivot and hanging shackle are stainless steel. The pivot has PTFE washers between the frame and arm to give a smooth but firm rotation.
The medallion was commercialy engraved and bears a latin inscription on the reverse side, "Astra splendida, finiensque longe" (Bright stars, distant horizons. Translation supplied by my Dad!).
The complete astrolabe took approx 120 hours spread over five months to complete, all the components being made by myself. A very enjoyable and satisfying project.
The background to the photo is the harbour of Barmouth on the Afon Mawddach Estuary on the edge of the Snowdonia National Park in North Wales.
Linear Astrolabe by Massimo Goretti, Arezzo, Italy (email@example.com)
An astrolabe reduced to a stick with engraved scales was described by Sharaf al-Dīn al-Tūsī (ca. 1135 - 1213). This rare astrolabe variation can be used to solve many astrolabe problems, such as measuring the altitude of the Sun or star, finding the length of the day, the time of sunrise/sunset in either equal or unequal hours and the approximate time from the altitude of the sun or a bright star of known coordinates. No old examples of this instrument are known to exist. The design theory and examples of how it can be used are described in some detail in The Astrolabe.
Massimo Goretti has made what is almost certainly the finest reproduction of a linear astrolabe ever made.
There is little information available on the details of the design and use of the linear astrolabe. Mr. Goretti combined information from an 1895 translation of a treatise by Abű al-Hassan Ali by Baron Carrà de Vaux (French), L'Astrolabe, Histoire, théorie et pratique (French) by Raymond D'Hollander, Traité de L'Astrolabe by Henri Michel, (French) and my book, The Astrolabe (English). Detailed knowledge of the planispheric astrolabe is needed to make or use a linear astrolabe and we had number of e-mail exchanges on some of the fine points.
The main component of his linear astrolabe is a lathe turned ebony rod about 27 in. (70 cm) long and 1.2 in. (30 mm) in diameter. The scales on the rod are about 20 in. (50 cm) long. The rod was engraved with the necessary scales using laser engraving to a depth of 1 mm and filled with white paint for contrast. The decorative caps and sights are of wild boar's tooth attached with brass ferrules. The threads are of silver rope and the thread positions are held in place with fabricated brass fixtures. His instrument is made for latitude 46°. Scales are included for measuring angles, almucantar meridian intersections, declination circle intersections, solar longitude and a special scale I provided that relates the Sun's longitude to right ascension and locates the right ascensions of several bright stars for use in finding the time. He has published a paper on the linear astrolabe in the June, 2010, issue (vol. 17, no. 2) of The Compendium, Journal of the North American Sundial Society.
Despite its apparent simplicity, the linear astrolabe is not very easy to use by one person, and two people are often required, but it is surprisingly accurate when used correctly. In depth knowledge of the plane astrolabe is needed to make or use one.
Mr. Goretti's linear astrolabe is a virtuoso performance in craftsmanship and science and is of museum quality. A perfectly useable linear astrolabe can be made with a dowel rod, paper scales taped to the rod, heavy thread and fishing sinkers. But it won't be as pretty.
Six Planet Orrery by Fred Jaggi of Cranston, RI (firstname.lastname@example.org)
An orrery is not, of course, an astrolabe, but Fred's accomplishment in making a working model deserves exposure. Following is Fred's description:
Peter Grimwood, a present-day orrery maker, gave me a diagram and wheel layout for a planetarium representing the six planets known since antiquity. The design is in the style of Benjamin Martin of Fleet St. ca 1750. It contains 14 gears, which allow the planets to orbit the sun in a steady circular path with an orbital period within 1/10th of one percent of the actual mean period. In those days, when calculations were done by hand, makers strived to calculate gear trains that would accurately represent natural orbits and the more advanced orreries produced elliptical paths and showed more planets and their satellites.
Last winter's project was to build Grimwood's planetarium. Unlike a clock, most of the gears are arranged in two stacks set at a fixed distance. A third shaft is fitted to accommodate the high gear ratio needed to represent Saturn's orbit. Six different modules, diametral pitch (DP), were used to allow the gears to mesh correctly. I had to make a fly cutter for each of the modules. The gears were cut using a homemade ball bearing spindle made up from pipe fittings and a dividing head. The tooth numbers on two of the gears are prime. For these, I pasted Excel spreadsheet grids on wooden disks attached to the dividing head. James E. Morrison adapted one of his astrolabe programs for my dial. I first thought about having the dial laser engraved locally, but the engravers said they were not able to laser engrave brass. I then turned to Hockerill Engraving in Devon, England who produced an inexpensive brass dial by chemical etching, which I then silvered. The dial has deep, sharp indentations, equivalent to mechanical engraving.
One turn of the dial represents two weeks motion and it's fun to watch Mercury race around in 87 days while Saturn moves at the almost imperceptible rate of nearly 30 years.
Mariner's Astrolabes made by Jeffrey Lock
Jeffrey Lock makes and restores old instruments to museum quality. See his web site at www.colonialinstruments.com. His work is unique in that he does almost all of his work using the same tools and the same techniques used to make the originals. Most of his work has been to make replacement parts for old instruments. It is impossible to tell which parts are original and which have been replaced or restored when he is finished.
The two Mariner's Astrolabes shown below were made from scratch starting with a block of brass. All of the finish work was done by hand, using only files and hand engraving. Here is Jeffrey's description:
As a restorer of scientific instruments, primarily surveying instruments of the 17th and 18th centuries, I have spent years studying the intricacies of their construction details. The most difficult task in the proper restoration and replication of instruments is mastering the effective engraving techniques employed by instrument makers from these early periods. The common denominator of the finest instrument makers, such as Schissler, Mercator, Gemini, and Humphrey Cole, was their complete mastery of engraving. When I initially started to teach myself to engrave, I had no idea how difficult, yet rewarding, that challenge would prove to be. Pictured here are two Mariner's Astrolabes that I engraved in the style of the English instrument maker, Humphrey Cole. They were hand-divided using a dividing plate I constructed for dividing compass needle rings.
These artists turned instrument makers accepted nothing less than perfection in all aspects of their work. The surest means to gain the most comprehensive understanding of these instruments and their construction methods is to fabricate them in the original manner, using original tools and procedures of the period in which the instrument was created. I currently have plans of building a large planispheric astrolabe in the style of the Louvain School and I intend to lay out and engrave in the original manner without the use of a computer-generated program. It is to this end that Jim Morrison's new book on the astrolabe is quite helpful. Other examples of my work and published articles can be found on my website, www.colonialinstruments.com.
Finished astrolabe before patination.
Final astrolabe after patination.
Horizontal Quadrant by Dr. John Davis, Ipswich, UK (email@example.com)
John Davis, who is very active in the British Sundial Society, has made a small batch of reproductions of a stereographic quadrant based on the horizontal projection (i.e. the projection plane is the local horizon rather than the celestial equator). This quadrant was originally published by Richard Delamaine (Delamain) in 1631. Delamaine had been a student of William Oughtred and his publication started a long debate between Oughtred and Delamaine on who originally defined horizontal projection instruments (see Turner, A. J., "William Oughtred, Richard Delamain and the Horizontal Instrument in Seventeenth Century England", Annali dell'Istituto e Museo di Storia della Scienza di Firenze, vi (1981), 99-125.). In fact, neither did, which makes the argument all the more amusing. Phillip Apian had published similar quadrants in de utilitate trientis in 1586, and such instruments had been documented in Islamic instrument treatises since the 13th century.
This form of quadrant is very easy to use to find the time from the sun's altitude. The sun's altitude is measured using the sights on the back of the instrument. The measured altitude on the rotating rule is aligned with the sun's declination for the day and the time is read from the hour arcs. A calendar for locating the sun's declination for a day is engraved along the lower right margin.
John designed the full-size replica in TurboCad with a horizon circle of radius of 100 mm. The quadrants are made of 16 swg (about 1/16 inch) thick brass, phosphor-bronze or nickel silver. Four full size and four half-size quadrants, along with rules and sights, fit on a 12 x 12 inch sheet. Printing uses dry film photoresist (which allows the use of positive masks ' black lines on a clear background). Masks are homemade on an inkjet printer. Exposure is 10 sec in a vacuum UV light box. Etching is in a homemade vertical bubble tank with ferric chloride at 40° C for, typically, 30 minutes. The plates are then stripped and the engraving filled with black enamel. Individual quadrants are cut out and assembled with bandsaw, files, burnishers, etc. The sights are soldered to the back of the quadrant.
Sculpture with astrolabe made by Laura DeAngelis, Kansas
City, Missouri, USA
One of the most unusual and beautiful implementations of a working astrolabe that I have seen is incorporated in a sculpture by Laura DeAngelis of Kansas City, MO. It is also the only ceramic astrolabe I have encountered. I collaborated on the sculpture to the extent of providing Laura with the line art of the astrolabe components, but the artistic realization is hers alone. The piece is one of a series of five sculptures representing the phases of life. Each of the pieces in the series incorporates an astronomical element. Laura has graciously supplied a description of the artistic background of the series and an overview of how the sculptures were made.
Over the years, my work has evolved from a search for elements that are both specific and universal. As a starting point, mythology, natural history, and science have been of particular interest because each contains a fixed model for perceiving different aspects of our relationship to the world within itself. My greatest interest lies in taking known factors such as these and weaving in my own history and understanding to create a personal micro-macrocosm.
This series of sculptures tell the story of a life in five phases, with each phase associated with a functioning scientific instrument. The instruments were chosen as a metaphor for recording life as it unfolds. The sculptures and instruments combine to bring us a clearer perception of ourselves and the forces that shape our existence.
Each piece in the series is based on a Janus figure. Janus was the Roman god of doorways and beginnings and is usually represented with two male heads, one looking forward and one back. Of the many interpretations of Janus, the one most fitting in this instance is that one head is looking to the future and one the past, to remind us that the future is a product of the past. The Janus figures in this series have a female and male side which correspond to the intrinsic male and female aspects present in all of us, and also to the male and female influences that resonate throughout our lives: parents, siblings, friends, lovers, marriage and children.
#1 Birth: Aurora, (Internal Sundial)
The opening scene of this story takes place in a mythological garden of paradise. Amongst exotic birds and flowers, a tree grows into the form of a lyre. This lyre is strung with only one string and when the female side is facing south this single string becomes a gnomon (Latin; meaning one who knows), which turns the interior of their body into a working sundial. To read the time, you look through the lyre on the male side to the hour marked by the shadow of the gnomon. Each day at noon, the shadow of the gnomon passes directly over a mythological egg, which is suspended above a small compass in the center of this internal world of quietude, signaling another beginning in this everlasting cycle.
#2 Youth: Odyssey, (Traverse Board)
Youth is depicted as an epic seafaring journey: a voyage of exploration and discovery marked by a series of milestones in the development of an individual. Crucial to the navigation of this journey is a traverse board, which enables the course of a ship or, in this case, two people to be traced without calculation or writing.
The chests of both figures are marked with the points of a compass, each rhumb-line being pierced radially with a sequence of small holes, which together form six concentric circles. Starting from the center, pegs are placed in the holes every hour according to the direction traveled. At the end of six hours, a visual record of the path taken is thus provided. When used by two people simultaneously, one on the male side and the other on the female side, it offers a wryly systematical way of charting the variable course of their passing days together.
The base is pierced with six additional horizontal rows of holes. The holes are numbered 1 to 5 and then 5, 10, and 15, followed by another three marked 1/4, 1/2, 3/4. Each row serves to indicate the distance traveled in miles during one hour, which can be tracked by the use of a pedometer. The three holes at the right of each row are for fractions of miles, while 5, 10, and 15 are for added miles. So, if you traveled 8 1/2 miles in hour 1, you would place one peg at # 3 and a second peg at # 5 and then a third at 1/2; all three numbers would then be added together to arrive at 8 1/2 miles. It is in this way, that at the end of 6 hours, a person can know just how far they have come and where they are heading.
#3 Middle age: Foreign Lands, (Terrestrial Map)
Middle age is represented by a map illustrating events from both the past and the future in one great convoluted tableau painted upon the body of the figure. On opposite ends of the sculpture, the central characters arrive by boat to an unknown region, a place full of uncertainties and imminent dangers, inhabited by strange beasts which must be confronted in order to pass through this land. Our protagonists appear again, this time in the present on the female side of the sculpture, each navigating their own way with the aid of a staff. The future of this epic unfolds on the male side of the figure, where at last, the two have combined their efforts. Their staffs have merged to become a divining rod, which they use to direct them to a rare treasure - a double-blooming columbine. It is accessible though a window in the legend of the map, which leads to the interior of the sculpture, where this elusive treasure has always been waiting for those who seek it.
#4 Future: Dreaming, (Astrolabe)
In the undulating countryside of Ravenna, Italy, our story looks towards the future. Integrated on the chests of the male and female sides of the sculpture is a planispheric astrolabe. The astrolabe is a historic astronomical instrument that offers the user an intuitive picture of the workings of the universe. This astrolabe is for the year 2021, and with it is possible to know and calculate the location of stars in relation to Ravenna and to determine a wide range of information relating to time, such as length of day or night for any day during that year. It commemorates the 700-year anniversary of Dante's and Beatrice's union amidst the stars as written in Paradiso, the last book of his Divine Comedy, which was finished in 1321 while in exile from Florence in Ravenna. In Paradiso, Dante's immortal love, Beatrice, guides him through the spheres of heaven, and it is rich with allusions to astronomy and cosmology - on the physical and spiritual order within the universe.
An astrolabe is made up of two parts, the front and the back. On the male side of the sculpture is the front of the instrument. Set into a blue background is a yellow piece that is carved and cut away, called the rete. The smaller circle the rete is the ecliptic circle, representing the course of the Earth around the Sun in a year. The space inside the ecliptic circle is carved into an anatomical heart and the arteries of the heart point to the fixed location of named stars. An astrolabe works by rotating the rete to simulate the movement of the sky, and when it is set to a specific date and time it offers a precise picture of the heavens for that time and location.
On the female side of the sculpture is the back of the astrolabe. The back is used to take measurements of the altitude of the Sun or a star and for determining the Earth's position in the ecliptic for a given date. Knowledge of the universe on the back of the astrolabes (the female side) is needed to orient the front of the astrolabe (the male side), uniting the two halves of the sculpture, giving meaning and substance to both.
#5 Death: Nocturne, (Celestial sphere)
Our story ends in an empty boat left adrift with only the starry sky above. You are left to contemplate what happens next. Their body has become the northern half of a celestial sphere, a virtual map of the heavens. The stars are each labeled by their Bayer letter and painted according to their magnitude. The male and female sides are divided by the Equinoctial Colure, which is a great circle passing through both the north and south celestial poles and the equinoxes. In essence, this means that when the Earth passes through the point where the two sides come together, both the day and the night will be of equal lengths, symbolizing an eternal balance of their inherent duality. Through the window in their chests a beeswax model of a double-sided vertebra is faintly visible; a vestige of a life now passed.
Technical information about the astrolabe and sculpture.
The sculpture is 17.5" x 13.5" x 9.5" and weighs 20 lb. (30 lb. with the base). It is entirely ceramic except for the metal alidade and rule. The female side was based on a live model. The rough face was then carved using imagination. The male face was carved, starting with the female profile. Making male and female faces with the same profile that are gender specific was very difficult.
A plaster mold of the entire sculpture (without the ears) was made in two parts (the ears were added later using a separate mold). A large sheet of clay was pressed into each side of the mold. The inside of the Janus was carved to resemble the dome of a Gothic cathedral. The Janus is removed from the mold after 24 hours and considerable refinement of details lost in the casting process is then applied.
When the sculpture is completely dry, it is fired to 1922 degrees F over four days. Glazing is applied when the sculpture has cooled. Several layers of glaze are required to get the desired color depth. A final glaze of wood ash and flux is applied and it is fired one last time.
The front of the astrolabe is 5.75 inches. The astrolabe plate is designed for Ravenna, Italy at 44 degrees, 25 minutes N, 12 degrees 12 minutes E, for the year 2021. The plate includes the almucantars and azimuth curves for each 5 degrees, unequal hour arcs and a crepuscular arc for -18 degrees. The limb uses a Renaissance style with a scale of degrees in four, 90 degree quadrants and a time scale with five minute divisions. The degree scale labels are 4.5 pt Palatino Italic and the Roman numeral hour symbols are Palatino with an aspect ration of 9:13.5.
The rete was designed by the artist and the supporting elements are in the shape of an anatomical human heart. The heart arteries support the star pointers. There are 32 star pointers, each of which is labeled. The ecliptic is divided for each five degrees and labeled with the zodiac signs. The original rete was carved from very fine grade porcelain, which allowed the required precision. A flexible rubber mold was then made from the master. The same clay as the Janus body was then applied to the mold and allowed to air dry from the back since rubber does not absorb water. Removing the rete from the mold was difficult because the clay shrinks as it dries, causing the cut out portions of the rete to fit more tightly in the mold. The completed rete was removed from the mold by bonding the rete to a sheet of clay while still in the mold and then peeling away the mold very, very slowly. The rete was separated from the sheet of clay by taking a taut piece of thread and running it parallel between the back of the rete and the sheet of clay. After finishing touches, the rete is dried between two small pieces of sheet rock to prevent warping.
The astrolabe back includes the zodiac, an eccentric calendar, shadow square and unequal hour conversion scale. The year for the calendar is in Roman numerals just inside the bottom of the calendar. The quotation between the calendar and zodiac is from Dante and translates as, "Love moves the sun and other stars." The back is 4.5 inches diameter.
The plate/limb and back were transferred to the sculpture using a material called Lazertran. The original black and white line art was colored and a color copy was made onto the Lazertran. The Lazertran is then briefly soaked in water until the thin film with the image separates from the paper backing. The image is then transferred to the sculpture and slowly fired at 500 degrees F to fuse the ink.
The base is not part of the sculpture.
Astrolabe made by Dr. John Jarvis, Eden Prairie, Minnesota,
John is a chemical milling professional and he applied his considerable knowledge of the process to making astrolabes with spectacular results. The style and quality of his astrolabes are as good as the best.
He supplied the following description:
Dr. Jarvis has been interested in astrolabes since the mid-70's after being introduced to them in a graduate astronomy course. He built his first astrolabe as a project for this course. His interest was rekindled in the mid-90s after purchasing a Personal Astrolabe from Janus.
The astrolabe described below is an example of his latest effort. The first attempt took several months before an acceptable device resulted including the time required to learn CAD, develop laminating techniques and make the etching equipment. The technique has been refined so that a device can be made in about a week of evenings.
John spends a good portion of his professional life designing chemical sensors, many of which are made using photo lithographic techniques that are deployed as a part of electronic instruments. It was the fusion of techniques used in this industry and a background in chemistry that provided the recipes for this project.
The astrolabe starts life as a set of 7.5 inch square of 0.040" thick 260 brass sheets cut from a larger sheet onto which photoresist is applied. After trying many different formulations, dry film photoresist, as used in the printed circuit board industry, was found to be the best and easiest to work with. It was applied with a typical office laminating machine that had been modified to accept thicker brass instead of paper. It took a bit of skill developed over many hours to laminate the photoresist to the brass without trapping any air bubbles.
The photomasks were designed using AutoCad and printed at 1600 dpi onto high resolution film at 1X. The photomasks were used to make contact prints onto the brass using a homemade vacuum frame and UV source. The purpose of the vacuum frame was to hold the photomask tight against the brass so that light cannot leak around the edges of the photomask and spoil the exposure.
The UV source was constructed using fluorescent black lights with some masking apertures to get quasi-collimated light. The collimation apertures serve to make the light rays parallel and hence get the highest contrast shadows from the film. The combination of the vacuum frame and source permit detail as small as 0.005" to be reproduced. After exposure, the plate is developed in a bath where the unexposed photoresist is removed.
An acid bath is used to perform the subsequent milling and engraving steps. Constant agitation of the solution and rotation of the brass is required to get a uniform etch rate. Eventually a purpose built etch tank was built to somewhat automate this process. Many different acid formulations were tried. Eventually either sodium persulfate solution or a stabilized sulfuric acid / hydrogen peroxide mix was found to work the best.
A typical plate was made in two steps. The first step involves chemical milling where the plate was exposed to a mask containing the outline of the part. The plate was developed and etched through from both sides in an acid bath. The plate was then relaminated with photoresist and the process repeated with a mask containing the artwork for the engraving.
At the completion of the engraving, a good bit of hand filing was required to finish the rough edges. The filing was followed with a hand rubbed polish and optionally inking the engraving marks to increase the contrast.
The astrolabe pictured was made in the general style of those by Jean Fusoris, an astrolabe maker who was active in the early 1400s. Astrolabes by Fusoris represent the perfect blend of function and style. Some astrolabes were so ornate as to be unusable. Many working instruments contained far less aesthetic appeal. The astrolabe was not an exact copy however.
Significant features are noted below:
1) The basic diameter of the device was 7 inches. The shackle extends the vertical dimension to 8 3/4 inches.
2) The recessed, single tympan was integrated into the limb. This reduced the overall complexity much like several of the later German instruments designed for use at single latitudes. The tympan shown was figured for 45 degrees North latitude (Portland, Minneapolis, Ottawa, Bordeaux, Milan, etc.) but will work very well a few degrees of latitude either side of 45°N. Tympans for 30, 35, 40, 45, 50, and 55 degrees North latitude have been made.
3) Altitude resolution was 2 degrees. Azimuth resolution was 5 degrees. Also included were unequal hour markings as well as crepuscular arcs for civil, nautical, and astronomical twilight.
4) The rete (star chart) was figured for epoch 2000 so the instrument reads correctly for modern times.
5) Stars were named with current common English names rather than Medieval Latin. Stars included were: Sirius, Rigel, Alphard, Regulus, Procyon, Betelgeuse, Bellatrix, Aldebaran, Menkar, Capella, Spica, Arcturus, Alphekha, Alkaid, Deneb, Scheat, Razalhague, Vega, Eltanin, Altair, Antares.
6) The back of the instrument contains the alidade, an eccentric calendar scale, the usual shadow square. A folded equation of time in the upper two quadrants replaces the traditional unequal hour conversion arcs. This latter feature was used to compute mean solar time from apparent solar time so with a simple correction for longitude, the device will read correct civil time.
Astrolabe made by Dr. Hasan Bilani, University of Aleppo,
This outstanding example of an Islamic astrolabe was made by Dr. Bilani in November 2000. It is not a reproduction of a specific instrument but is in the style of a typical, high quality Islamic astrolabe. It was designed using AutoCAD and was engraved by chemical milling. It required about two months to manufacture. It is made of brass and is about eight inches in diameter and 5.5 mm thick and weighs 900 gm. There are 23 stars precessed to the current epoch. There are six plates provided but only two can be held in the mater at a time. The quote from the Koran on the throne (kursi) is "...and by the stars (men) guide themselves". It is a beautiful instrument.
Plates: Damascus, Alepppo, Tripoli, Libya, Dubai, Medina, Mecca, Amman, Al-Quds, Al Manama, Kuwait, Khartoum, Rome, Toulouse
Plate Latitudes (degrees, minutes): 15,33 / 21,25 / 24.30 / 25,14 / 26,12 / 29,20 / 31,46 / 31,57 / 32,54 / 33,30 / 36,12 / 41,53 / 43,33
Resolution: Altitudes - 3 deg, Azimuths - 5 deg.
Stars: Cetus, Procyon, Sadr, Sirius, Alphard, Capella, Demonstar, Denebola, Marfik, Minkar, Ras Al Hague, Algol, Altair, Betelgeuse, Dogstar, Spica, Nair ql Saif, Aldebaran, Deneb Kaitos, Arcturus, Keid, Vega.
Back: Calendar and solar longitude, Scale of sines and cosines, shadow square, cotangent scale, scale of sun's altitude for Mecca, Al-Quds, Al Manama, Kuwait, Khartoum, Toulouse and a qibla (direction to Mecca) for Aleppo, Tripoli, Al-Quds, Al Manama, Toulouse.
Mariner's Astrolabe made by Ian Bovington, Sydney, Australia (firstname.lastname@example.org)
Ian Bovington used the Mariner's Astrolabe template from this site to make a reproduction instrument. His description of the instrument and its construction follows:
The aim in constructing a marine astrolabe was to gain a hands-on insight into the difficulties of astrolabe construction, even though the astrolabe was a simple mariner's astrolabe, and gain experience in using the instrument. I have gained a true appreciation of the astrolabe through using this instrument. All the celestial altitudes for my Masters Degree history project where taken with this marine astrolabe and all calculations were made with The Classic Edition of The Personal Astrolabe.
This marine astrolabe is 210mm wide by 230mm high, the plate and alidade both 6mm in thickness. The plate and alidade are constructed of marine grade aluminium. (Scrap plate from STA Ferries dockyard, Sydney Australia). The centre pin is of steel turned from a 1/4inch Whitworth bolt on the author's lathe. The pin is tapped into the centre of the plate with a lock nut on the back of the plate providing tension for the alidade. A felt washer sits between the alidade and the plate. The ring attached to the throne is made of mild steel.
The plans for the plate of this instrument were taken from James E. Morrison's website. These plans were scaled up to the maximum width of an A4 sheet of paper, printed and glued onto the 6mm aluminium sheet with PVA glue. The outline of the instrument was then engraved onto the aluminium using the plans as a guide. The engraver used was a Burgess model 72. The degree ticks were stamped using a small screw driver as a punch, and a hammer. The numbers were engraved using the engraver. The outline and internal cutaways were then cut out using a power jig saw with a metal cutting blade. The edges were then filed and sanded. The alidade was cut out in a similar way. The central hole of the plate was then drilled and tapped (1/4 inch). The throne and hanger were constructed and drilled at this time. The alidade is of the authors own design, the sights are of 1 mm plate aluminium with notched sights, these were then glued to the alidade with epoxy glue. A line is scribed through the centre of the alidade from sight to sight to allow shadow Sun sights to be taken (not shown on the image). After the parts of the instrument were cut out all the parts were cleaned and buffed polished on an electric buffer.
In use this marine astrolabe proved to be reasonably accurate. The sighting method required some getting used to and the weight of the instrument, somewhat lighter than an original brass astrolabe, proved tiring after a period of use. The astrolabe has to be held at arms length to align the back sight correctly. It should also be noted that, this may seem obvious, a light is required to see the sights of a night time. To illuminate the sights I used a pen with a LED light built into it (Jaycar Electronics). The astronomers of the middle ages must have used a candle or small lamp, either way some juggling is required to take a sight at night time. To take a Sun sight the instrument is held at eye level parallel to the body with the Sun's shadow projected down the alidade, the notch of the sight lining up with the scribed line on the alidade. The readings are then read off the scale on the altitude scale of the instrument. This practice was found not to be as accurate as taking a star sight.
Astrolabe made by Wolfgang Abratis, Malente, Germany (email@example.com)
Wolfgang Abratis has made two wonderful astrolabes, a classic planispheric instrument and a universal astrolabe of Gemma Frisius' "astrolabum catholicum" type. Following is the documentation sent to me by Mr. Abratis:
I have always been fascinated by the inherent beauty of astrolabes. In 1994, after having read about the use of the astrolabe, I finally decided to have a go and build one myself.
Given the complexity of the task, I wanted my astrolabe to last at least as long as its historic predecessors. Thus, the most commonly used materials like cardboard, wood or copper were out of the question. What was left was bronze, or rather brass.
Astrolabes like that could only be found in the hands of the nobility or astrologers at an important court. However, it was instruments like this that survived, while many cupreous or wooden astrolabes just vanished.
After visiting the small astrolabe exhibition at the Hamburger Museum für Kunst und Gewerbe, I decided that the style was to be that of the late renaissance, this era being the astrolabe-making heyday.
My astrolabe was to have a diameter of 200 mm (7 3/4 ") and a thickness of at least 5 mm (1/5"). As I did not intend to create a replica of an existing instrument, I was free to choose which scales and tables I would incorporate into the design aside from the mandatory ones. Primarily, I wanted a scale for the solar declination. Although it can be determined with the regula and the ecliptic circle, I decided that this was too imprecise for position determination. The declination scale is the innermost on the dorsum.
I had some real fun when designing "my" coat of arms on the dorsum. This being a quite common style element in renaissance and baroque, I did not want to stand back. However, neither did I have a family crest nor the vaguest notion about heraldy, so I started reading on the subject and designed a so-called "speaking" coat of arms.
It consists of a stylized walking wolf ("Wolfgang") on an equally stylized raft (Latin ab ratis: "coming from the raft"). The whole is framed by an escutcheon with a crown and the motto: "FLOREBO QVO FERAR".
I opted for a rete with 50 stars. Aside from the fixed stars, I also incorporated the supernova discovered by Tycho Brahe in 1572, and the comet C/1996 O1 (Hale-Bopp). The last two had, of course, are only for decoration.
I chose to have 5 plates of 0.8 mm thickness each. First and foremost, I needed one for the latitude of my location in Northern Germany (54°N ). The other I constructed for 51°N. Having always been intrigued by the history of the Caribbean, and since astrolabes were used when the Silver Fleets sailed, I chose a range of latitudes that covers the entire Caribbean.
For the actual construction, I used the line etching technique. The back of the brass plates are covered with ground asphalt, while the front side is coated with a water resistant marker. Then, the lines are drawn with a needle, scraping off the thin coating where necessary.
I "branded" all major components with the inscription "INCESSVS LVPI FECIT MDXCV(I)", meaning "The wolf's walk (i.e. Wolfgang) has made this in 1595/6". Of course, the name and the year have to be taken with a grain of salt.
Sawing out the rete, the ring between limb and dorsum and the plates was the fun part. Honestly, I never ever had such a muscle ache in my life. I used a fretsaw, the very same tool the astrolabists of old used.
I then put the parts (limb, ring and dorsum) on a hot stove plate and soldered them together. After cooling, I also riveted them together, just to make sure.
As a finish, I decided to gold plate the parts to protect them from oxidation. The pertinent literature recommends stainless steel as the anode. As I had rather large parts to finish, I used a high grade steel frying pan. I applied voltage and obtained a 24K gold plating effectively reducing the risk of tarnishing the metal. Also, my fried potatoes have this golden color since then ;-)
A friend was so kind as to sew a red velvet bag with gold cord for transporting the astrolabe in proper style.
After final assembly, I was stunned by the astrolabe's weight: About 1.7 kg (55 oz.)! This has led me to the conclusion that - contrary to popular belief - no stars were used for latitude calculation. Having been a sailor in the merchant marine for several years, I find it exceedingly hard to believe that any person should be willing to lift such a weight at arm's length and still try to sight a second magnitude star (Polaris) through a 2 mm (1/16 ") diameter or less hole in the middle of the night. To do so is a feat even on solid ground, but from the deck of a rocking galleon this is next to impossible.
It is, however, very easy to "shoot" the sun's altitude. What's more, you may carry the astrolabe at waist level, making handling even easier. Only during landfall, stars were used for position determination. An inaccuracy of only one degree would result in an error of 60 nautical miles, which could spell the difference between sailing in friendly waters or running aground on some treacherous reef.
Addendum: I have since built another astrolabe (diameter 15 cm) as well as other baroque navigational instruments. The gross building time for this one was 400 hours. Working on the project has given me invaluable insights into various areas such as astronomy, heraldry, art, history, metal processing etc.
The end? Hardly. I have been contemplating a brass mariner's astrolabe lately...